Heathcock, JACS 107, 3731 (1985) and J. Med. Chem. 30, 1858 (1987) disclose the preparation of the keto-phosphonate A ##STR4## (which is used in the total synthesis of compactin) by separating by HPLC the diesters B-C ##STR5## where in B, R.sub.1 is --OSi(CH.sub.3).sub.2 --t--C.sub.4 H.sub.9 and R.sub.2 is H and in C, R.sub.1 is H and R.sub.2 is --OSi(CH.sub.3).sub.2 --t--C.sub.4 H.sub.9 and then converting the isomer B to keto-phosphonate A in 5 steps to obtain an overall yield of 34%. Due to the difficulty of the HPLC separation of B and C, this technique can only be used to prepare relatively small quantities of keto-phosphonate A, for example, less than 0.5 g.